Furnace Troubleshooting

You could always go with another Coleman type unit, but those are expensive. Many people on here myself included have switched over to an inexpensive digital thermostat. I bought a cheap non programmable thermostat at Walmart and it runs on AAA batteries and it does the job well. But mine only controls the heat.

As said above these thermostats do not have a low and high fan speed. Some people just wire them on high fan and some add a micro switch to the side of the thermostat to control the fan speed. There are a few write ups here and on the net to help with the wiring.

Link to digital thermostat

Link to one of many posts about wiring.

I replaced the POS Coleman T-stat with a cheap Honeywell manual digital heat cool stat from HD. I found the instructions on here, but don't know where. It was awhile ago. I do know that the wire colors were different.

The Honeywell has only one fan position, so if you want high and low, a separate switch must be installed.

The digital stat works MUCH better than the Coleman with the "slide" temp lever.

So . I'm convinced that it's the thermostat. Now. Any suggestions on
a replacement?
and thanks to all for your advice.

I do have power to the red wire. If I gave that impression
on my post my apologies. I am on shore power. I have tested the
incoming wires from the wall to the furnace and only get power to one
wire and not the other. At the thermostat I get power at red and none to
The others when on furnace mode. On a/c mode I get power to the blue
wire and my a/c and fan work.

Edit: ****I just read your post again and I see you have power at your red wire. If this is true then you should be able to disconnect the red and white wires from the thermostat. Then in your hands just touch them together and the furnace should fire. If so then I would suspect the thermostat. ****

Leaving original text below as it might help someone else in the future.

The wire that goes to the R terminal (sometimes they use the RW terminal) should have 12 volts (battery voltage) on it. I'm assuming in your trailer that's the red wire you are referring to. The W terminal goes to the heater. (I'm assuming that's a white wire.) All the thermostat does in heat mode is connect the two wires together just like you did by joining them with your hands. So if you have no 12 volts on the red wire then the furnace won't fire no matter what thermostat you have. Here's a couple more tests you can try and they're free too. :)

First thing when checking voltage is you have to know what you are checking for. Take your meter to the battery and measure the voltage across the positive and negative terminals. This will give you battery voltage. Some people might tell you that all you need is 12 volts and you are good in your checking. But what if your battery reads 12.76 volts when you check it, and your heater reads 12.2 volts? That would be a sign of something wrong. But if you have no idea what voltage the battery has then 12.2 might look good as it's 12 volts.

Since you have no power at the thermostat I would suspect a bad fuse. look at the fuses in the fuse box. A careful inspection will reveal that there are two holes on the back of each fuse, one on each side of the amperage rating. (silver dots on either side of the 10 in the picture below).


These holes allow you to probe the fuse for voltage without disconnecting it from the holder. Check for voltage from each hole in the fuse to a good ground or the negative post of the battery. Anything less than battery voltage on either side is bad (either fuse or holder).
If you have battery voltage on both sides of the fuse you're going to have to find out why you are not getting battery voltage at the thermostat.

You could also use a long wire and grab 12 volts off something else like a ceiling light and run it to the W wire at the thermostat. If the furnace fires then connect this temporary wire to the R (Or RW) terminal of your thermostat and check the furnace again.

I think you thermostat is fine and you somehow lost the 12 volt power to the furnace that is needed to run the heater.

beergardens wrote:
If the fan doesn't even come on when there's demand for heat, I wouldn't consider the regulator or propane system as a possible cause.

I agree. Thanks for pointing me in the right direction.
Now. Should I purchase the same thermostat or a diff one?
If a diff one, which one do you suggest. I currently
have the coleman mach with the fan fan control. It is a 6 wire model.

If the fan doesn't even come on when there's demand for heat, I wouldn't consider the regulator or propane system as a possible cause.

opnspaces wrote:
If I follow correctly you can run the furnace while it's on the bench? Then when you put it back in the trailer it does not work correctly?

Before you buy a thermostat you might try a test of removing the thermostat off the wall and connect the wire on the terminal labeled R (or RW) to the wire on the terminal labeled W. If your theory is correct the Furnace should run and heat. Let it run for a minute then disconnect the wires and it should shut off. Now let it cool for a few minutes and connect the wires again. If it works flawlessly then you most likely have a bad thermostat.

Did that and nothing happened. Checked all wires on diff modes and only the red and blue wire had any power to it when running a/c. Used multimeter on all wires. No juice to white wire coming from thermostat in any mode.

hhernandez13 wrote:
ill ck thermostat the way opnspaces suggested first. then go from there and ck regulator. my tanks are newly refilled and my stove works. so ill figure out a way to bypass regulator on trailer with propane line that has regulator that i used for bench test.

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Burners may still work with a bad regulator. Either test the regulator or turn on your high volume burner(stove) and see if you noticed a difference between that and the other regular (2) burners.
That was my friends problem...
Happy trails,